Fatigue Reliability Analysis For Titanium Pressure Hull Of Deep Manned Submersible

Pressure hull of deep submersible as a loading-bearing structure is the primary factor to ensure the normal work of the whole system, and the reliability of which is a direct impact on the performance of the submersible. In this paper, the author predicts the fatigue life of the pressure hull and then analyzes its reliability based on fracture mechanics, which could provide references for the structural design and optimization of the submersible.Dive data of Alvin is chosen as a reference to determine the fatigue load spectrum of the deep submersible because Alvin has the same design maximum dive depth of 4500 meters. Gumbel distribution is more suitable to be used to create the probability model for dive depth distribution of deep submersible compared with other distributions, and then the fatigue load spectrum of pressure hull could be concluded by the transformation between pressure on the submersible and the dive depth.Then the theory of plates and shells and the finite element method are used to analyze the stress level of the pressure hull which could be used to check the strength of the pressure hull. The result shows that the strength of the pressure hull meets the requirement to submersible.The author uses fracture mechanics to estimate the fatigue life of titanium pressure hull. Crack model based on the Paris model and Brown-Hobson model are used to do uncertainty analysis of the crack propagation. The results meet the design requirement of the pressure hull. At last, considering accuracy and efficiency quadratic response surface method without cross terms is chosen as the approximation method of fatigue reliability for the pressure hull. And then calculate the reliability index for the hull and analyze the parameter sensitivity in the two models, which could provide a reference for the selection of parameter values and dive depth. Compared with Paris model the total fatigue life model consider the stage of short crack propagation which could describe the full process of crack propagation more precisely, so the model is more suit for the analyzing of pressure hull.